Isolation valves or full independent Doubles

[Dhboner]

Free flow isn't the only way regs fail.

No but is the most likely issue on a dive with well-serviced equipment (at least here in the frozen north).

 

[WhiteSands]

In sidemount you have access to ALL of your gas even in the event of a regulator free flow. Since the tank valves are pretty much at your armpits you can "feather" the offending valve and continue to access the gas in that tank.

I am honestly curious about how this works, and if it is really a practical or workable solution?

Do sidemount divers diving in overhead environments plan for penetration with 1/3 gas of one tank, or 1/3 gas of both tanks?

If planning for 1/3 gas of both tanks, and if a failure or incident happened at the deepest point of penetration, you will then need all the gas in both tanks (especially if solo diving) and I guess you will have no other choice but to feather the valve to try to breath out all the gas in the "failed" tank.

Imagine a scenario in a wreck where there is a silt out, and you had to hold on to the line with one hand, your buddy's arm with another, how would you feather the tank? Or if solo diving and no buddy is present, perhaps one hand on the line, and the other stretched out in front to feel for obstructions...

Or any other similar scenario where you need the use of both hands for extended periods of time, e.g. shooting and reeling an SMB? How are these scenarios mitigated?

Thanks.

 

[Aquavelvet]

No, you've miscalculated the remaining gas in the above scenario. If you have used 1/3 of the gas in each tank, then the remaining gas in either tank should be enough to get you out. Provided that there isn't adverse flow on the way out. This suggests that diving on thirds is not as conservative as might be necessary under some conditions. This is covered in the Cave courses that you would need to take.


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[Akimbo]

In sidemount you have access to ALL of your gas even in the event of a regulator free flow. Since the tank valves are pretty much at your armpits you can "feather" the offending valve and continue to access the gas in that tank.

So can I, but I also have the option to cross-connect regulators.

 

[WhiteSands]

No, you've miscalculated the remaining gas in the above scenario. If you have used 1/3 of the gas in each tank, then the remaining gas in either tank should be enough to get you out. Provided that there isn't adverse flow on the way out. This suggests that diving on thirds is not as conservative as might be necessary under some conditions. This is covered in the Cave courses that you would need to take.

Hmmm yes you are right.

Assuming each tank is 11L and both are filled to 200bars, that's 4400L of total available gas. If you use 1/3 of both tanks for penetration, you have used up 1467L of gas. That leaves 2933L. If you lose one of the tanks due to some serious failure (unfixable regulator, tank valve, etc.) you have 1467L of gas left.

It seems kind of risky to me as that leaves you with hardly any reserve for lost buddy search, lost line search, dealing with emergencies or in a rare case of double failures, air-sharing with your buddy on the way out. It seems in all of these worst case scenarios, it will be very hard to feather and try to breath off the remaining tank in an already very stressful situation.

 

[Aquavelvet]

Your numbers are still slightly off, but you understand the issue. One of the conclusions we take from this is the need to keep the gas in the two tanks closely balanced. This is not for trim, but to preserve an adequate reserve, in case gas in one of the tanks becomes lost or inaccessible. The other conclusion is that it would be safer to turn the dive prior to reaching 1/3.


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[wedivebc]

Hmmm yes you are right.

Assuming each tank is 11L and both are filled to 200bars, that's 4400L of total available gas. If you use 1/3 of both tanks for penetration, you have used up 1467L of gas. That leaves 2933L. If you lose one of the tanks due to some serious failure (unfixable regulator, tank valve, etc.) you have 1467L of gas left.

It seems kind of risky to me as that leaves you with hardly any reserve for lost buddy search, lost line search, dealing with emergencies or in a rare case of double failures, air-sharing with your buddy on the way out. It seems in all of these worst case scenarios, it will be very hard to feather and try to breath off the remaining tank in an already very stressful situation.

How many simultanious failures can you plan for? Typically one is the norm.

 

[Remy B.]

So can I, but I also have the option to cross-connect regulators.

I'm currently in the Process of TDI AN, and I got me a hybrid wing, that is recreational but can be customized a lot, right know it has two 7L 200Bar metal tanks on it, I will add some special D-rings that remain strait to help me with releasing the sling deco-gas bottles, but I actually want to invert my tanks some like Akimbo configuration, since I actually can access quicker the tank valves on the bottom than on the top, I'm just thinking in practicality and easy operation, it will require longer hoses for the regulators and wing and drysuit hoses but it seems way easier to access the valves and less chance to entanglement and/or easier to get out of the entanglement since there is no valves or regulators, my instructor say it was a old way of configuration, did not like it, but at the same time he did not say not to do it kind of.

Yes a custom protector around the valves is a most.

What do you think ??

Re-breathers use this configuration, does not seem a big issue, why it is not so popular now days beside hose length issue. I don't see any real drawback of configuring my setup like this, only minor stuff but, I may missing something, this weekend it just will be practicing so I will not meet with my instructor, but I like your opinions as well, before I go more in deep detail about the kind of configuration I want with my instructor.

 

[decompression]

Inverted twinsets are/were popular in the UK and elsewhere, not so much North America. There are off the shelf valve protectors, not sure of the manufactures off hand. I'd like to see a valve drill done on a set of inverted twins but I think most are ID so actually it would be easier. I'm curious as to what you'll end up using.


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[Akimbo]

... What do you think ?? ...

Not sure if you are asking me specifically or what the question is. Valve-down doubles is my preferred configuration and I am working a second generation protector similar to the one in the photo.

Inverted twinsets are/were popular in the UK and elsewhere, not so much North America. There are off the shelf valve protectors, not sure of the manufactures off hand...

These are the only ones I could find on the market: VALVE PROTECTORS

I chose to make mine because I wanted more protection, reduced entanglement risk, and a more comfortable fit.